This invention relates generally to magnetic disk drives, more particularly to magnetoresistive (MR) read heads, and most particularly to spin-dependent tunneling (SDT) read sensors and methods of making the same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk drive 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, a magnetic disk 16, supported for rotation by a drive spindle S1 of motor 14, an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 typically includes an inductive write element with a sensor read element (shown in FIG. 1C). As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to "fly" above the magnetic disk 16. Various magnetic "tracks" of information can be read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk drives is well known to those skilled in the art.
FIG. 1C depicts a cross-sectional view of a magnetic read/write head 24 including a read element 32 and a write element 34, which is typically an inductive write element. Exposed edges of the read element 32 and the write element 34 define an air-bearing surface ABS, along a plane 35, which faces the surface of the magnetic disk 16.
Read element 32 includes a first shield SH1, an intermediate layer 39 which serves as a second shield SH2, and a read sensor 40 located between the first shield SH1 and the second shield SH2. Read elements commonly make use of a phenomenon termed the magnetoresistive effect (MRE), where the electrical resistance R of the read sensor 40 changes with exposure to an external magnetic field, such as magnetic fringing flux from magnetic disk 16. The incremental electrical resistance .DELTA.R is detected by using a sense current that is passed through the read sensor 40 to measure the voltage across the read sensor 40. The precision and sensitivity of the read sensor in sensing the magnetic fringing flux increases as the ratio of .DELTA.R/R increases. Also, larger resistances result in larger voltages measured across the read sensor 40 which, in turn, results in greater effectiveness of the read sensor. Thus, it is desirable to maximize both the output voltage and .DELTA.R/R.
Types of magnetoresistive effects utilized in the read sensor 40 include the anisotropic magnetoresistive (AMR) effect and the giant magnetoresistive (GMR) effect. A particular type of effect is the spin-dependent tunneling (SDT) effect, which can be used in an SDT sensor. A schematic of such an SDT sensor is illustrated by the read sensor 40 in FIG. 1D. As is shown, the SDT read sensor 40 can include a tri-layer, sometimes referred to as a tri-layer tunnel junction, having a first ferromagnetic (FM) layer FM1 and a second ferromagnetic layer FM2, which are separated by an insulating layer INS. These layers are oriented substantially parallel to the shields SH1 and SH2. Thus, when the sense current I is injected to the SDT read sensor 40 between the shields SH1 and SH2, the current can travel substantially perpendicular to the layers FM1, FM2, and INS. In other words, the SDT read sensor can operate in current perpendicular to plane (CPP) mode. Write element 34 includes an intermediate layer 39 that functions as a first pole (P1), and a second pole (P2) disposed above the first pole P1. P1 and P2 are physically and electrically attached to one another by a backgap portion (not shown) distal to the ABS. A write gap 46 is formed of an electrically insulating material between P1 and P2 proximate to the ABS. Also included in write element 34 in the space defined between P1 and P2 are conductive coils 48 disposed within an insulation layer 50.
In the SDT read sensor 40, the ferromagnetic layers FM1 and FM2 can act as electrodes between which the sense current I passes through the insulating layer INS, which is sometimes referred to as the tunnel barrier. The relative directions of the magnetizations M1 and M2 of the ferromagnetic layers FM1 and FM2, respectively, can be influenced by external magnetic fields, thereby changing the resistance of the SDT read sensor 40, which can be detected with the sense current I. More specifically, when the magnetization of one of the ferromagnetic layers is anti-parallel to that of the other ferromagnetic layer the SDT effect results in a higher resistance across the SDT read sensor, with a lower resistance being experienced when M1 and M2 are parallel to each other. Typically, SDT read sensors exhibit .DELTA.R/R of up to 18-30% and output voltages higher than 10 mV, which is higher than that produced with many other types of MR read sensors. Thus, while advances in magnetic disk and drive technology are resulting in magnetic media that have increasingly higher area density, corresponding increasing read sensor performance needs can be met by the higher .DELTA.R/R and higher output voltages of SDT read sensors.
The SDT read sensor 40 can be formed by successive deposition over a first lead (here the first shield SH1) of different materials to form the first FM layer FM1, the insulating layer INS, and the second FM layer FM2. Because the SDT read sensor is operated in CPP mode, the .DELTA.R/R is particularly sensitive to the interfaces between the layers of the SDT read sensor (interlayer interfaces). To provide interlayer interfaces with minimal pin holes and impurities, and therefore higher .DELTA.R/R, FM1, FM2, and INS can be successively deposited in a one-pump-down process.
The sensor layers 42 are then etched using typical processes to form the FM1, FM2, and INS, over which a second lead, here the second shield SH2, is deposited. Such etching is needed to provide suitable read sensor dimension control to meet increasingly high magnetic media area densities. Unfortunately, if the etching is performed after all three materials have been deposited in a one-pump-down process, material which has been etched away from one of the three layers can redeposit on the exposed remaining portions of the other layers (along the sidewalls 41). This can often result in the redeposition of portions of the first and/or second ferromagnetic layers such that an undesirable electrical path, or short circuit, is formed between FM1 and FM2 along the sidewalls 41. With such a short circuit path, the SDT sensor 40 may not effectively produce the spin-dependent tunneling phenomenon, and therefore exhibits reduced sensor effectiveness. Theoretically, short circuits could be minimized through the use of complex, expensive, and/or time-consuming processes to limit such redeposition, however, this would not be cost-effective for commercial production of SDT read sensors.
Later in the fabrication process, the layers of the SDT sensor 40 are lapped substantially perpendicularly to the sensor layers 42 to form the air bearing surface ABS. Unfortunately, during this process, material from a facing (or front) surface (or edge) of one of the various layers can be smeared over the other layers. If the material from FM1 and/or FM2 is smeared between the two layers, such material can also form an undesirable short circuit path between them. Further, as the read sensor 40 thickness H becomes increasingly smaller, to accommodate higher area densities, FM1 and FM2 may become closer together, thereby increasing the likelihood of smearing between them. As can be understood by those skilled in the art, the problems of edge redeposition and smearing, and their concomitant reductions in read performance, can also be encountered in the fabrication of other read sensors that operate in CPP mode.
Therefore, to provide the benefits of the spin-dependent tunneling effect in a read sensor, a read sensor and a method for making the same are desired which have a high degree of interlayer interface control while avoiding the formation of short circuit paths between conductive layers of the read sensor. Also, it is desired that such a read sensor be fabricated less expensively and more quickly while using current read sensor process technologies. Further, to meet increasingly higher magnetic media area density, such a read sensor is desired to be fabricated with a high degree of read sensor dimension control.